The present invention concerns therapeutic compositions and methods for the treatment of cancer.
The present invention relates to therapeutic compositions and methods for the treatment or diagnosis of diseases or conditions related to EGFR expression levels, such as cancer. The following summary is not meant to be complete and is provided only for understanding of the invention that follows. This summary is not an admission that any of the work described below is prior art to the claimed invention.
The epidermal growth factor receptor (EGFR) is a 170 kDa transmembrane glycoprotein consisting of an extracellular `ligand` binding domain, a transmembrane region and an intracellular domain with tyrosine kinase activity (Kung et al., 1994). The binding of growth factors to the EGFR results in down regulation of the ligand-receptor complex, autophosphorylation of the receptor and other protein substrates, leading ultimately to DNA synthesis and cell division. The external ligand binding domain is stimulated by EGF and also by TGF.alpha., amphiregulin and some viral growth factors (Modjtahedi & Dean, 1994).
The EGFR gene (c-erbB1), is located on chromosone 7, and is homologous to the avian erythroblastosis virus oncogene (v-erbB), which induces malignancies in chickens. The v-erbB gene codes for a truncated product that lacks the extracellular ligand binding domain. The tyrosine kinase domain of the EGFR has been found to have 97% homology to the v-erbB transforming protein (Downward et al., 1984).
EGFR is overexpressed in a number of malignant human tissues when compared to their normal tissue counterparts (for review see Khazaie et al., 1993). The gene for the receptor is both amplified and overexpressed in a number of cancer cells. Overexpression of the EGFR is often accompanied by the co-expression of the growth factors EGF and TGF.alpha., suggesting that an autocrine pathway for control of growth may play a major part in the progression of tumors (Sporn & Roberts, 1985).
Growth factors and their receptors may play a role in the development of human brain tumors. A high incidence of overexpression, amplification, deletion and structural rearrangement of the gene coding for the EGFR has been found in biopsies of brain tumors (Ostrowski et al., 1994). In fact the amplification of the EGFR gene in glioblastoma multiforme tumors is one of the most consistent genetic alterations known, with the EGFR being overexpressed in approximately 40% of malignant gliomas (Black, 1991). It has also been demonstrated that in 50% of glioblastomas, amplification of the EGFR gene is accompanied by the co-expression of mRNA for at least one or both of the growth factors EGF and TNF.alpha. (Ekstrand et al., 1991).
The amplified genes are frequently rearranged and associated with polymorphism leading to abnormal protein products (Wong et al., 1994). The rearrangements that have been characterized usually shown deletions of part of the extracellular domain, resulting in the production of an EGFR protein that is smaller is size. Three classes of deletion mutant EGF receptor genes have been identified in glioblastoma tumors. Type I mutants lack the majority of the external domain, including the ligand binding site, type II mutants have a deletion in the domain adjacent to the membrane but can still bind ligands and type III, which is the most common and found in 17% of glioblastomas, have a deletion of 267 amino acids spanning domains I and II of the EGFR.
In addition to glioblastomas, abnormal EGFR expression has also been reported in a number of squamous epidermoid cancers and breast cancers (reviewed in Kung et al, 1994; Modjtahedi & Dean, 1994). Many patients with tumors that overexpress the EGFR have a poorer prognosis than those who do not (Khazaie et al., 1993). Consequently, therapeutic strategies which can potentially inhibit or reduce the aberrant expression of the EGFR receptor are of great interest as potential anti-cancer agents.